Guillermo Largo is a character from Chaff. He was born in Lima (Peru) into a "middle-class, nominally Catholic, very mildly leftist family" in 1980. His father was a journalist with El Comercio and died from a cerebral blood clot in 2029. At the time of Chaff, Guillermo's mother was still alive at 78 years old, working as an attorney for an international mining company. He had an elder brother (a retired surgeon) and a younger sister (a primary-school teacher). He married and divorced thrice and was known to be childless.

He studied in Harvard (and at least briefly in Switzerland) and was first employed by the Department of Energy after he finished his PhD in 2005. After that, he held several other research posts split between government agencies, the biotechnology industry and academia.

He moved to Bethesda, Maryland and proceeded to live there for a generous timespan. As an employee, he was "classified as brilliant but unsound - a potential security risk, but far too talented and productive to be wasted" and subject to routine surveillance, though this became increasingly spotty.

It's strongly insinuated that politically speaking, he was an anarcho-communist.

He disappeared (along with "some highly classified genetic tools") into El Nido de Ladrones in 2035 (after "thirty years with an unblemished record" (including "no tax fraud, no gambling debts") and cited to be fifty-five), which resulted in a mercenary being sent to capture him - the story of Chaff.

At time of his disappearance, "his household computers hadn't been systematically tapped for almost twenty years", leaving the protagonist of Chaff disappointed, given it seemed like all digital records were wiped by Guillermo before he left.